Heat oven to 350F (180C) with oven rack in middle.,Spray a nonstick 10-cup (47-L) Bundt pan generously with nonstick cooking spray.,To Make the Filling:,Mix brown sugar and cocoa in a small bowl and cut in butter until mixture resembles coarse crumbs with some pea-sized pieces.,To Make the Cake:,Combine flour, baking powder, baking soda, and salt in a medium bowl.,Beat butter and sugar in bowl of a heavy-duty mixer on Medium speed until creamy, scraping down bowl once or twice.,Add sour cream, vanilla, and eggs and beat until smooth.,______,Reduce mixer speed to Low, add the flour mixture, and beat just until the flour disappears.,Stir in chocolate chips.,Spoon half of the batter into prepared pan and sprinkle with filling.,Cover with remaining batter, spreading evenly to cover the filling.,Keep filling away from sides of pan to prevent sticking.,Bake 35 to 50 minutes or until a toothpick inserted in center comes out clean.,Cool 10 minutes on wire cooling rack.,Remove cake from pan (see Notes) and cool completely.,Sprinkle a little powdered sugar and cocoa over coffee cake.